1. Field of the Invention
The invention generally relates to material delivery systems and methods of metering and delivering a material to a system or process and methods of calibrating such systems and methods. Particularly, the invention relates to material delivery systems and methods of metering and delivering a material to a fluid catalytic cracking (FCC) unit and methods of calibrating such systems and methods.
2. Description of the Related Art
Some industrial processes, such as fluid catalytic cracking systems, deliver one or more specified amount of a material such as a catalyst(s) or additives. FIG. 1 is a simplified schematic of one embodiment of a conventional fluid catalytic cracking system 130. The fluid catalytic cracking system 130 includes a FCC unit 110 coupled to catalyst or additive addition system, etc. 100, an oil feed stock source 104, an exhaust system 114 and a distillation system 116. Catalyst from the catalyst addition system 100 and oil from the oil feed stock source 104 are delivered to the FCC unit 110.
The catalyst addition system 100 may include a main catalyst injector 102 and one or more additive injectors 106. The main catalyst injector 102 and the additive injector 106 are coupled to the FCC unit 110 by a process line 122. A fluid source, such as a blower or air compressor 108, is coupled to the process line 122 and provides pressurized fluid, such as air, that is utilized to carry the various products, such as a catalyst, additive, equilibrium spent catalyst, catalyst fines, etc. from the injectors 102, 106 through the process line 122 where they are combined with oil from the oil feed stock source 104 and delivered into the FCC unit 110.
FIG. 2 is an embodiment of a conventional additive injector 106. The additive injector 106 includes a pressure vessel 220 and a low pressure storage vessel 240.
Some material delivery systems 100 (i.e. catalyst injection system, catalyst or additive addition system, etc.) use a vessel located on load cells which is capable of metering a specific amount of a catalyst, etc. Weight based systems can vary based on ‘gain-in-weight’ or ‘loss-in-weight’ measurement. ‘Gain-in-weight’ system is sometimes described by its weight function as the load cells monitor a ‘gain’ in weight as catalyst is added to the delivery vessel. Once the target weight is reached, further additions to the delivery vessel are stopped. The ‘loss-in-weight’ system fills a delivery vessel with catalyst, but the entire catalyst contained in the delivery vessel is not immediately delivered to the industrial process. In ‘loss in weight’, the delivery vessel is filled with some quantity of catalyst which is greater than the desired delivery dose to the industrial process. The ‘loss in weight’ of the delivery vessel is monitored and the resulting desired addition to the industrial process is made. The amount of loss in weight, or the difference in weight between the pre- and post-delivery points represents the specific desired quantity of catalyst delivered to the industrial process.
Weight based systems vary in accuracy, precision of the metering and overall reliability of the system. For example, if the pressure vessel 220 is supported by any of the structural components surrounding it, other than the load cells 210 (such as pipes, electrical conduits, and the like), those components will prevent the load cells 210 from accurately measuring the weight of catalyst added to the pressure vessel 220, and ultimately into the FCC unit 110. Therefore, in order to obtain a reasonably accurate measure of the catalyst, the pressure vessel 220 is not be supported by other components of the system.
To isolate the pressure vessel 220 from the components coupled thereto, flexible connectors, such as bellows 230, are used to couple the pressure vessel 220 to the low pressure vessel 240, the process line 122, and other surrounding components. The bellows 230 allow the pressure vessel 220 to “float” on the load cells 210 so a more accurate reading may be obtained. However, use of flexible bellows 230 does not reliably insure accurate weight measurement of the pressure vessel 220. For example, the weight of the pressure vessel 220 is still slightly supported by the flexible bellows 230—a problem compounded by the fact that a plurality of bellows 230 must be utilized to isolate the pressure vessel 220 from the various components coupled thereto. Therefore, the determination of the weight of the catalyst added to the pressure vessel 220 is still not accurate.
Furthermore, the weight based systems in industrial processes are prone to repeated maintenance failures, particularly when continuous use to deliver consistent performance to FCC units is needed. Frequent repeated maintenance may be due to a large amount of moving parts, high cyclic requirements of the system to fill and discharge relatively small quantities, and load cells, typically in multiples of 3-4 per unit, which fail with age or drift in calibration Any maintenance time results in a consequent FCC down time because of not receiving the catalyst for which the weigh based addition system is supposed to deliver. Such maintenance ‘down time’ has performance and economic implications on the industrial process.
Thus, a need still exists for an automated and reliable manner, method and system to accurately and consistently deliver a specified quantity of a material to an industrial process.